This invention relates to a nuclear reactor. In more detail the invention relates to a compact, air-cooled reactor useful for power generation. And in still more detail the invention relates to a nuclear reactor designed for aircraft propulsion.
While the reactor according to the present invention will be described particularly in connection with its use as a part of a power plant for aircraft, it will be appreciated that the reactor can be used for other purposes such as in stationary power plants.
The primary objectives of designers of nuclear power plants for aircraft are compactness because of the weight of required shielding and high performance. Because of the high performance requirements for aircraft nuclear reactors, an approach different from that which was successful in the construction of submarine and surface marine vessels is necessary. Two approaches have been followedxe2x80x94a direct-air-cycle system and an indirect-cycle system. The indirect-cycle system employs heat exchangers to transfer heat from a liquid metal to a working fluid. Although the reactor is smaller than a direct-air-cycle system and therefore requires less shielding, the miles of tubing and thousands of welds required make of the reactor an extremely challenging engineering task.
Direct-cycle plants may be subdivided into open-cycle plants or closed-cycle plants. Although the latter offer theoretical advantages, particularly for extremely high-performance power plants, the additional problems created by the necessity for containing the working fluid in closed-cycle plants militate against their immediate utility.
Accordingly the reactor according to the present invention is gas-cooled and is designed to operate in direct, open cycle with a gas turbine.
Such reactors have previously been designed but in general they lack the performance characteristics necessary to make them potentially useful for aircraft propulsion.
It is accordingly an object of the present invention to develop an improved, direct open-cycle reactor using relatively well-known materials under conditions of low temperature and stress and yet achieve compactness and high performance.
It is a further object of the present invention to develop an air-cooled nuclear reactor wherein the distance the air must travel through the core is reduced to a minimum.
It is a further object of the present invention to develop an air-cooled reactor wherein the moderator is overcooled by placing it upstream of the fuel.
It is also an object of the present invention to develop a reactor in which coolant air bathes all possible components.
These and other objects of the invention are attained by a novel direct-cycle nuclear reactor incorporating reversed, folded flow. Folded-flow reactors are defined as reactors in which the frontal area of the fuel elements is so large and the heating path so short that the core must consist of many layers of fuel elementsxe2x80x94hence the term xe2x80x9cfoldedxe2x80x9d. Folded flow compacts the heat exchanger region of the core into a small volume. A reversed-flow, folded-flow reactor is one in which coolant approaches each of the many layers of fuel from a direction parallel to the layers, and after passing through the fuel, returns in the direction from which it came. Flow reversal reduces core size by reducing the air voids necessary to bring air to and from the fuel elements.
To obtain reversed, folded flow a plurality of a rectangular slab porous fuel elements are disposed radially about a central island. Wedge-shaped porous moderator elements are disposed adjacent one face of each fuel element. The layers are oriented in alternate fashion so that the moderator elements face each other and the fuel elements do likewise. These elements are disposed so that coolant air can enter the core travelling inwardly, make a right-angle turn to pass through the moderator layers and then the fuel layers and then make another right-angle turn leaving the core in the reversed direction.